Today, we are familiar with contactless chip cards or contactless SIM cards which allow contactless transmission of data between the data storage medium and associated read unit. These are frequently used for storing data. Normally, the power required for operating the data storage medium is also transmitted contactlessly by the read unit. In line with the power and data transmission methods used, contactless ID systems are referred to as RFID (Radio Frequency Identification) systems.
Power is supplied to the data storage medium and data interchange takes place between the data storage medium and the read unit using magnetic or electromagnetic fields.
A read/write unit typically contains a radio-frequency module (transmitter and receiver), a control unit and a coupling element for the electronic data storage medium.
Any communication between the data storage media themselves takes place via a read or write unit (transmitting and/or receiving station), which performs the master function in the communication.
Contactless data storage media always operate in slave mode and cannot communicate with one another directly.
Read and write operations on a contactless data storage medium are handled strictly according to the master/slave principle. All the activities of the read unit and of the data storage medium are initiated by the application software. In a hierarchic system structure, the application software is thus the master, while the read unit as the slave becomes active merely upon read/write commands from the application software. In order to execute a command from the application software, the read unit starts to set up communication with the data storage medium. In this context, the read unit is now the master for the data storage medium. The data storage medium thus responds exclusively to commands from the read unit and never becomes active autonomously.
The basic task of a read unit is thus to activate the data storage medium, to set up communication with the data storage medium and to transport the data between the application software and a contactless data storage medium. All the special features of contactless communication, that is to say connection setup, anticollision or authentication, are handled by the read unit alone.
Passive contactless data storage media are becoming increasingly widespread in many areas, particularly on the consumer market. Up until now, it has not been possible for two contactless data storage media to be able to interchange data directly without the use of a read/write unit.